1. Field of the Invention
The present invention relates to an image forming apparatus that corrects density of an output image by checking a density change occurred in a printed matter, an image forming method, and a computer program product.
2. Description of the Related Art
A conventional print-on-demand printer typically includes, in addition to an image correction device, an image inspection apparatus that checks a density change occurred in an output image. When a density change has occurred, the printer performs a correction process to suppress the change, thereby ensuring accurate color and density, each of which is an element that determines quality of a printed matter. Techniques for the density correction process are broadly divided into a first technique and a second technique, as described below.
In the first technique, a density correction process is performed by forming a density correction patch on a photosensitive drum or an intermediate transfer belt at a portion outside an area where a print image is formed and detecting a density of the density correction patch (See Japanese Patent Application Laid-open No. 2008-158504, for example). In the second technique, a density correction process is performed by forming a density correction patch on a recording sheet and detecting a density of the density correction patch (See Japanese Patent Application Laid-open No. 2007-274438, for example). Automatic tone correction (ACC), which is generally employed by a multifunction peripheral (MFP), in which density is detected by using a scanner, can alternatively be employed.
In the conventional first technique described above, density of a patch on an output sheet is not actually measured, and accordingly, the first technique is less accurate in correcting density than the second technique. However, the first technique is advantageous in that image density correction is performed without interrupting output of a user image (or, even when the output is interrupted, an interrupted period of time can be very short) because the density correction patch is formed outside an image forming area of a print image.
In contrast, in the second technique, density of a patch on a printed sheet is measured by actual measurement; accordingly, the second technique has a benefit of keeping accuracy in density correction. However, when the second technique is adopted, productivity is decreased because the second technique requires the density correction patch to be output on the recording sheet. Under these circumstances, an optimal control method has been required for the density correction processes.